1. Field of the Invention
The invention relates to the preparation of alkylene carbonates, also known as glycol carbonates, by reaction of alkylene oxides with carbon dioxide, and more particularly to such processes in which catalysts are employed.
2. Description of Related Methods
The reaction of alkylene oxides with carbon dioxide in the presence of a catalyst is known. U.S. Pat. 2,773,070 to Lichtenwalter et al. discloses a process for preparing alkylene carbonates using an ammonium halide catalyst. U.S. Pat. No. 2,873,282 to Mc Clellan discloses the use of certain quaternary ammonium compounds to catalyze the reaction of alkylene oxides and carbon dioxide. W. J. Peppel, in "Preparation and Properties of the Alkylene Carbonates,"Industrial and Engineering Chemistry, vol. 50, no. 5, pp. 767-770 (May 1958), provides an overview of the various methods then known for the preparation of alkylene carbonates.
It appears that most of the known processes employ halogen-based catalysts. For example, U.S. Pat. No. 4,786,741 to Sachs teaches a process for preparing alkylene carbonates that employs a catalyst selected from the group consisting of organic quaternary ammonium halides organic quaternary phosphonium halides, organic sulfonium halides, and organic antimony halides. European Patent Application 0 297 647 claims a process wherein alkylene carbonates are prepared using a catalyst comprising an alkali or alkaline earth metal halide. Japanese Patent Application Number 63-181765 also discloses a method for the preparation of alkylene carbonates using an alkali halide catalyst. Halide-based catalysts, however, tend to contaminate the alkylene carbonate product with halogen compounds. Other known catalysts may include a strong base that deactivates or decomposes the carbonate, or that causes the epoxide to react with epoxide rather than with carbon dioxide.
Applicants have discovered that metal phthalocyanine salts provide good yields of alkylene carbonates. Applicants have further discovered that it is possible to obtain good yields using non-halogenated metal phthalocyanine salts, and thereby avoid contaminating the alkylene carbonate product with halogen compounds.